This invention relates to a tool for grinding toothed workpieces using dressable grinding tools that are optimized with regard to the maximum tool diameter by collision surfaces, like interference contours or limitations from preprocessing, such as tool run-out.
Known tools for generating grinding of tooth systems always have a tool holding mandrel or flange by means of which the tool is held in the grinding machine. This mandrel/flange requires a certain minimum diameter in order to have the necessary stability. The tool(s) is(are) fitted on this mandrel/flange and generally fastened to the mandrel/flange by laterally arranged fastening elements. So that a collision between the tool and holding mandrel/flange does not occur during grinding, the usable tool diameter only begins after this region. A certain minimum tool diameter results due to this design principle and due to the coating thickness necessary in the abrasive coating for an economical grinding process.
Modern transmissions contain, in addition to the classic gears with bores (“bored workpieces”), input-, intermediate-, and drive shafts as well, which have one or more toothings which are directly connected to the shaft and/or come from a raw material. A characteristic of these components is a workpiece geometry that has so-called collision teeth, i.e. further toothing, a shaft collar, another interference contour next to the toothing to be processed, or toothing that does not end in an end surface but instead runs out with a radius. This must be considered with regard to the design of the toothing tool already during machining before heat treatment (roughing with hob or form cutter). During the hard-fine machining necessary after hardening, the tool diameter may often only have maximally the same diameter as during the machining before heat treatment.
In general, these workpieces are processed after the heat treatment using the following hard-fine machining processes.    1. Generating grinding using electrically coupled CBN worm grinding wheels    2. Profile grinding using electrically coupled CBN profile grinding wheels    3. Gear honing    4. Generating grinding using dressable cutting material (aluminum oxide, CBN or similar)    5. Profile grinding using dressable cutting material (aluminum oxide, CBN or similar)
If dressable tools are used (processes 4 & 5), then, due to the collision situation at grinding wheels and worm grinding wheels and a conventional tool design, the installation space is lacking for the necessary coating thickness which is required in order to always generate new, fresh, easy to cut grinding tool surfaces, even during multiple dressing of small cutting material coatings. Due to this circumstance, dressable profile- and generating worm grinding wheels are not economical in this application, even though these cutting materials are used extremely successfully in “collision-free” tooth systems.
For this reason, these tooth systems have often been hard-fine processed using processes 1-3 up until now. This is due to economic reasons and because tools made from dressable cutting materials can be more easily re-profiled. However, a process with dressable tools would be desirable. It is, however, necessary for this purpose to realize a certain minimum coating thickness in order to obtain an economically usable tool. At the same time, the tool mandrel requires a minimum diameter so that the necessary stability and stiffness is realized. These two limiting conditions define or delimit the possible radial installation space for the tool.
German document DE 101 04 410 A1 discloses a tool for generating grinding of tooth systems during which the grinding tool consists of a bearing ring and an abrasive body which is fitted on a conical mounting flange. In this way, the grinding tool is fixed without play. The deformation resistance of the bearing ring is thereby greater than that of the abrasive body. Due to this arrangement, displacements and deformations of the worm grinding wheel caused by centrifugal forces are minimized. Disadvantageous in this embodiment are the spatial requirements required in order to accommodate all function elements in the tool and at the same time guarantee the necessary stability of the holder.
International PCT publication WO 94/19135 discloses a single-part galvanically-coated tool having two different portions. These two portions are coated with hard materials in order to undertake different grinding tasks during the hard-fine machining process. The grinding tool comprises a conical mounting sleeve with which it is fitted on the round tool mandrel and tightened. This embodiment also requires a certain minimum height for the tool. In connection with a stable round mandrel for the tool, this results in a certain minimum tool diameter. In this arrangement of the tool, the tool diameter and/or the coating thickness are no longer changed thereby, since no dressing of the abrasive coating takes place. If this tool is worn out, it must first be decoated in order to be subsequently newly recoated. Disadvantageous in this embodiment is that changes to the profile shape of the grinding tool can only be generated during the manufacture thereof. During hard-fine machining, such changes or re-profilings are no longer possible due to the low coating thickness of the abrasive material. This is only possible using dressable grinding tools.
German document DE 10 2004 020 364 A1 likewise describes a tool for generating grinding of tooth systems having a multi-part grinding tool with dressable abrasive bodies. In this case, a multi-part tool is described in which different abrasive bodies are clamped on a common base mandrel.